1. Field of the Invention
The present invention relates to an optical waveguide plate to be used for a display which consumes less electric power, and which has large screen brightness. In particular, the present invention relates to a structure of the optical waveguide plate to be used for the display for displaying, on a display surface of the optical waveguide plate, a picture image corresponding to an image signal by controlling leakage light at a predetermined position on the optical waveguide plate by controlling the displacement action of an actuator element in a direction to make contact or separation with respect to the optical waveguide plate in accordance with an attribute of the image signal to be inputted.
2. Description of the Related Art
Those hitherto known types of display include, for example, cathode ray tubes (CRT) and liquid crystal display devices.
Those types of displayes known types of cathode ray tube include, for example, ordinary television receivers and monitor units for computers. Although the cathode ray tube has a bright screen, it consumes a large amount of electric power. Further, the cathode ray tube involves a problem that the depth of the entire display device is large as compared with the size of the screen.
On the other hand, the liquid crystal display device is advantageous in that the entire device can be miniaturized, and the display device consumes a small amount of electric power. However, the liquid crystal display device involves problems in that it is inferior in brightness of the screen, and the field angle of the screen is narrow.
In the case of the cathode ray tube and the liquid crystal display device, it is necessary for a color screen to use a number of picture elements (image pixels) which is three times a number of picture elements used in a black-and-white screen. For this reason, other problems occur in that the device itself is complicated, a great deal of electric power is consumed, and it is inevitable to increase the cost.
In order to solve the problems described above, the present applicant has suggested a novel display (see, for example, Japanese Laid-Open Patent Publication No. 7-287176). As shown in FIG. 9, this display includes actuator elements 100 arranged for respective picture elements. Each of the actuator elements 100 comprises a main actuator element 108 including a piezoelectric/electrostrictive layer 102 and an upper electrode 104 and a lower electrode 106 formed on upper and lower surfaces of the piezoelectric/electrostrictive layer 102 respectively, and a substrate 114 including a vibrating section 110 and a fixed section 112 disposed under the main actuator element 108. The lower electrode 106 of the main actuator element 108 contacts with the vibrating section 110. The main actuator element 108 is supported by the vibrating section 110.
The substrate 114 is composed of a ceramic in which the vibrating section 110 and the fixed section 112 are integrated into one unit. A recess 116 is formed in the substrate 114 so that the vibrating section 110 is thin-walled.
A displacement-transmitting section 120 for obtaining a predetermined size of contact area with an optical waveguide plate 118 is connected with the upper electrode 104 of the main actuator element 108. In the illustrative display shown in FIG. 9, the displacement-transmitting section 120 is arranged such that it is located closely near to the optical waveguide plate 118 in the ordinary state in which the actuator element 100 stands still, while it contacts with the optical waveguide plate 118 in the excited state at a distance of not more than the wavelength of the light.
The light 122 is introduced, for example, from a lateral end of the optical waveguide plate 118. In this arrangement, all of the light 122 is totally reflected at the inside of the optical waveguide plate 118 without being transmitted through front and back surfaces thereof by controlling the magnitude of the refractive index of the optical waveguide plate 118. In this state, a voltage signal corresponding to an attribute of an image signal is selectively applied to the actuator element 100 by the aid of the upper electrode 104 and the lower electrode 106 so that the actuator element 100 is allowed to make displacement in conformity with the ordinary state and the excited state. Thus, the displacement-transmitting section 120 is controlled for its contact and separation with respect to the optical waveguide plate 118. Accordingly, the scattered light (leakage light) 124 is controlled at a predetermined portion of the optical waveguide plate 118, and a picture image corresponding to the image signal is displayed on the optical waveguide plate 118.
The display described above is advantageous, for example, in that (1) it is possible to decrease the electric power consumption, (2) it is possible to increase the screen brightness, and (3) it is unnecessary to increase the number of picture elements as compared with the black-and-white screen when the display is allowed to have a color screen.
By the way, the optical waveguide plate 118 included in the display is composed of a transparent material such as glass and acrylic resin, because it is necessary that the light 122 introduced from a light source 126 is totally reflected.
When the optical waveguide plate 118 is composed of glass, there is no problem in the case of a small-sized display screen of the display. However, when the display screen has a large size, problems occur in that the weight of the optical waveguide plate 118 is increased, and the glass is expensive. A method may be conceived, in which the optical waveguide plate 118 is made to be thin. However, a thin optical waveguide plate 118 causes other problems that it is difficult to introduce the light 122, and the display brightness becomes nonuniform (the central portion becomes dark).
In order to solve the problems described above, it is conceived that a transparent material having a light weight such as an acrylic resin is used for the optical waveguide plate 118.
However, as shown in FIG. 10, when the optical waveguide plate 118 is composed of an acrylic resin material, the surface tends to suffer scratches "a". Further, such an optical waveguide plate 118 is insufficient in rigidity as compared with the glass plate, and hence waviness and warpage are apt to occur, making it impossible for such an optical waveguide plate 118 to be applied to a large-sized display.